Compiling diverse evidence such as limited accumulation of soil organic matter, high phenol oxidative and proteolytic enzyme potentials due to microbial activity, and symbioses between plants and fungi, the fungal loop hypothesis suggests that carbon and nutrients are cycled in biotic pools rather than leached or effluxed to the atmosphere during and between pulses of precipitation.
In arid ecosystems, there is low total precipitation and high variability in size of rain events (pulses) within and between years.
Therefore, in arid ecosystems where precipitation falls during the hot season, fungi are likely the most important contributors to nutrient cycling due to their tolerance to temperature and ability to persist during long dry periods.
[1] In arid ecosystems, many primary producers, such as grasses and biological soil crusts, form symbioses with fungi.
[7] Dark septate endophytes (DSE) are also common in many aridland plants and are hypothesized to perform similar roles as mycorrhizal fungi.
One study used isotopic labeling to trace where nitrate and glutamate moved when provided to biological soil crust or to grass foliage a distance away.